Bones connected at a joint are connected by soft tissue, which includes ligaments. In joint surgery, the stability (lability) of a state of connection between a first bone and a second bone that are connected by soft tissue at a joint is checked. More specifically, in joint surgery, a surgeon checks the stability of the state of connection between the first bone and the second bone by relatively moving the first bone and the second bone and ascertaining the state of movement. For example, in the case of joint surgery for a knee joint, the surgeon checks the stability of the state of connection between the tibia and the femur by relatively moving the femur with respect to the tibia or relatively moving the tibia with respect to the femur, and ascertaining the state of the movement.
An instrument disclosed in Patent Document 1 is known as an instrument that can be used in knee joint surgery to check the stability of the state of connection between the tibia and the femur. The instrument disclosed in Patent Document 1 is constituted by a femur-attached member that is attached to the femur, and a jig body that abuts against a proximal end face of the tibia and a distal end face of the femur that are formed by excision. The femur-attached member and the jig body are connected so as to be able to relatively move in a direction perpendicular to the proximal end face of the tibia and be locked at any relative position, in order to cause a state of tension in the soft tissue that connects the tibia and the femur.
More specifically, in the instrument disclosed in Patent Document 1, the femur-attached member has a rod portion that is inserted into the femur along an axis thereof from the distal end face of the femur, and a cylindrical portion that extends in a direction perpendicular to the axis. The jig body has a spacer arranged on the proximal end face of the tibia, and a movable block that is fixed to the spacer in a removable manner and abuts against the distal end face of the femur. Furthermore, the movable block has a drive screw capable of rotating while meshing with the cylindrical portion of the femur-attached member. The drive screw is rotationally driven by a hexagonal wrench. Due to the drive screw being rotationally driven, the femur-attached member and the movable block are driven so as to relatively move with respect to each other. Thus, the instrument disclosed in Patent Document 1 is configured to be able to relatively move the tibia and the femur in separating directions and cause a state of tension in the soft tissue. The surgeon uses this instrument to relatively move the tibia and the femur in separating directions and check the stability of the state of connection between the tibia and the femur.